HYDROPHYLLE.E-HYDRUS. 



upon the nature of their food, which consists of vege- 

 table matter, although it has been stated that they will 

 also feed upon small aquatic mollusca and insects ; 

 but this observation was made by M. Miger upon 

 insects in a state of captivity. M. Esper has made 

 another observation, which shews the weakness of 

 these insects when compared with the other water- 

 beetles. He had confined an individual of the largest 

 species of this family, Hydrous piceus, in a glass of 

 water with a Dyticus marginalia, not more than half 

 of its size the former, nevertheless, fell an easy prey 

 to the latter ; which, having detected a vulnerable 

 part between the head and thorax, greedily devoured 

 it. Unlike the Dytiddce, these insects exhibit a great 

 degree of care for the preservation of their race, in 

 the mariner in which they deposit their eggs ; which, 

 instead of being laid at random in the water, are 

 united into a mass, and enclosed in a silken cover, in 

 which they are carried about by the female beneath 

 her body until she is able to meet with a convenient 

 spot for their reception, and which is ordinarily the 

 stem of some aquatic plant upon which she attaches 

 her mass of eggs above the surface of the water, 

 whereby they are defended from the attacks of her 

 enemies : in this situation the eggs hatch, and the 

 young larvie tall into the water. Such is the mode 

 adopted by the smaller species ; but the larger ones 

 (Hyd. piceus, &c.) differ somewhat. Like the former 

 they are provided with spinnerets at the extremity of 

 the body, and they spin a bag of pure white silk, of a 

 very large size, having on one side an elevated twig 

 or branch, in which the eggs, to the number of fifty or 

 sixty, are enclosed in an upright position, and it is not 

 until they have been hatched several hours, that the 

 young larva; make their escape. It appears, more- 

 over, from the recently published researches of Lyon- 

 net, that the female also employs in the construction 

 of her nest the fibres of aquatic plants. This, how- 

 ever, is contrary to the remarks of M. Miger, who 

 informs us that the use of the elevated branch of the 

 nest, and which is raised above the surface of the 

 water, as it floats about, is of service in conveying 

 air into the mass of eggs enclosed in the nest. The 

 larvae are large fleshy grubs, furnished with six legs, 

 which, as well as the head, are of a scaly nature ; the 

 former being of a curious form, nearly flat above, and 

 rounded below, which gives it the appearance of being 

 turned upside down. They respire by the assistance 

 of two slender appendages at the extremity of the 

 body. When arrived at its full size, the larva quits 

 the water, and burrows into the soft adjacent earth, 

 where it forms a cell, having the inside smoothened, 

 and in which it becomes a pupa, not exceeding one- 

 half of its previous length ; the larva of H. piceus 

 being three inches long, and the pupa only one and a 

 half. The abdominal segments of the pupa are fur- 

 nished with long lateral filaments or soft spines ; its 

 thorax is also armed with three curved spines on each 

 side. By these, and by the appendages at the ex- 

 tremity of the body, the pupa is stated to be raised 

 from the surface of the cell, whereby it is prevented 

 from being in constant contact with the damp earth. 

 On arriving at the perfect state, the insect again seeks 

 the water, in which it constantly resides, but it is 

 necessary that it should come from time to time to 

 the surface to obtain a supply of fresh air. Authors 

 had remarked that at such times, unlike the Dyticida:, 

 which respire by the extremity of the body, it pro- 

 truded its antenna: out of the water, and that they 



811 



were applied against the body when it retired again 

 below the surface : but the recent observations of 

 M. Audouin have shewn, that it was by this motion 

 that a bubble of air is carried along the under side of 

 the thorax until it arrives at the abdominal spiracles. 

 The majority of these insects are of small size, but 

 the family comprises a few species, which are amongst 

 the largest of the aquatic coleoptera. The genera 

 are, Hydrophilus, Hydrous, Philhydrus, Tropisternus, 

 Stcrnolophus, Hydrobius, Volvulus, Berosus, and Limnc- 

 bius ; to which Mr. Stephens adds Spcrchcus. In the 

 typical genus, Hydrophilus, the sternum is spined, the 

 pectoral carina being bifid, and the antennae are ob- 

 tuse at the tips. The type is the Hydr. Caraboides, 

 Linnaeus, a very common species, found in the stag- 

 nant ponds and ditches, being about three-quarters of 

 an inch in length, and of a shining black colour. 



HYDROPHYLLE^E. A natural order of ele- 

 gant herbaceous plants, natives of North America. 

 The order contains five genera, viz. Hydrophyllum, 

 Phacclia, Eutoca, Varronia, Nemojihila, and Ellisia. 

 These associated genera very closely resemble the 

 Boraginidece and Heliotropidae : the twin-celled basal 

 nectary, and one-celled ovarium, will, however, suffi- 

 ciently distinguish them. The fungous-stalked Pla- 

 centcB is also a very peculiar and characteristic struc- 

 ture. 



HYDROUS, (Linnaeus). A genus of pentame- 

 rous coleopterous insects, belonging to the family 

 Hydrophitidte, and diti'ering from Hydrophilus, in hav- 

 ing the antennas acute at the tips, the pectoral carina 

 of the prosternum simple, and the terminal joint of 

 the male tarsi, which is dilated into a large triangular 

 plate. The type, H. piceus, is the largest of our 

 British water-beetles, being an inch and a half long, 

 of an olive black and shining colour. It is found in 

 ponds and stagnant waters, but not very commonly. 



HYDRUS (Hydra). A genus or rather family of 

 serpents, which are all inhabitants of the seas or rivers 

 of warm countries. The name was originally applied 

 allegorically to a monster which Hercules is fabled to 

 have subdued ; and though Linnaeus transferred the 

 name to one of the simplest of all animals, an inhabi- 

 tant of the fresh waters which can be multiplied by 

 dividing the body into segments, those who treat of 

 the natural history of serpents very generally apply 

 it as the distinctive name of water-serpents, whether 

 these happen to be poisonous or not. They are 

 found in greatest abundance in the seas and rivers of 

 the south-east of Asia, of Australia, and of some of 

 the adjoining countries. In their teeth they resemble 

 the Colubrcs and Acrocohordi, but they have generally 

 a smaller number of teeth in the external range ; and 

 some have the first of this row on each side much 

 larger than the others, and perforated for the purpose 

 of conveying their poison, which is of a very deadly 

 nature in some of the species, into the wound inflicted 

 by the tooth. They live generally under the water ; 

 and in this they are distinguished from some other 

 species which are often found swimming on the sur- 

 face, but which seldom or never dive to the bottom, 

 as the true hydras are in the habit of doing. They 

 feed almost exclusively upon fish. Some of them 

 grow to a very large size ; and many, indeed the 

 greater part, are remarkable for the brilliance of their 

 colours and the elegance of their markings. Cuvier 

 divides them into three subgenera : 



Hydroph'is, which chiefly infest the seas, rivers, and 

 other waters of Bengal and the adjoining countries 



